# Role of PRC2 in the stochastic expression of Aire target genes and development of mimetic cells in the thymus

## TL;DR

This study shows how PRC2 helps Aire control gene expression and develop mimetic cells in the thymus, using single-cell techniques.

## Contribution

The study reveals PRC2's dual role in Aire-mediated gene expression and mimetic cell development, independent of Aire.

## Key findings

- PRC2 represses chromatin to enable Aire's stochastic gene expression in thymic cells.
- PRC2 independently controls the development of mimetic cells in the thymus.
- The role of PRC2 in mimetic cell development is more prominent than its role in Aire function.

## Abstract

This study highlights the contribution of PRC2 to Aire-mediated stochastic gene expression and the development of mimetic cells through various single-cell approaches. The genomics data utilized in this work serve as a valuable resource for advancing research on Aire.

The transcriptional targets of Aire and the mechanisms controlling their expression in medullary thymic epithelial cells (mTECs) need to be clarified to understand Aire’s tolerogenic function. By using a multi-omics single-cell approach coupled with deep scRNA-seq, we examined how Aire controls the transcription of a wide variety of genes in a small fraction of Aire-expressing cells. We found that chromatin repression by PRC2 is an important step for Aire to achieve stochastic gene expression. Aire unleashed the silenced chromatin configuration caused by PRC2, thereby increasing the expression of its functional targets. Besides this preconditioning for Aire’s gene induction, we demonstrated that PRC2 also controls the composition of mTECs that mimic the developmental trait of peripheral tissues, i.e., mimetic cells. Of note, this action of PRC2 was independent of Aire and it was more apparent than Aire. Thus, our study uncovered the essential role of polycomb complex for Aire-mediated promiscuous gene expression and the development of mimetic cells.